1. Field of the Invention
The present invention relates to tools, gauges, fixtures, and the like for use in the aerospace industry, and particularly to a propeller blade seal positioning gauge for marking the locations of the circumferential seals for installation on the shank of a controllable pitch propeller blade prior to reassembly of the propeller.
2. Description of the Related Art
Propellers for large and complex aircraft are constructed with blades that can rotate axially within their sockets in the propeller hub or barrel, as the hub may be known in larger propeller assemblies. This allows the angle or pitch of the blades to be adjusted for different flight conditions, e.g., flatter pitch for greater engine RPM at slower speeds for takeoff, and coarser pitch for relatively lower RPM at higher airspeeds, as in cruise flight. The propellers of most turboprop-powered aircraft may also be adjusted into what is known as “beta” mode, i.e., a negative angle of attack, for aerodynamic braking after landing in order to shorten the landing distance.
The blade and hub assembly requires lubrication and seals for the lubrication. In addition, the actual control of the angular blade positions in the hub or barrel is controlled by hydraulic fluid pressure in many engine and propeller types and configurations. The seals about the shanks of the propeller blades must be positioned precisely due to the centrifugal forces that tend to throw the lubrication from the propeller hub. The relatively short length of the shank of the propeller, which mates with the short passage or receptacle in the propeller hub or barrel, results in extremely large mechanical, centrifugal, and aerodynamic forces acting through this relatively small interface between the blade and hub or barrel.
Accordingly, the installation of propeller shank seals is an exacting task that requires great care and patience. For example, it has been found in U.S. Navy propeller overhaul shops and aircraft intermediate maintenance facilities (AIMD) that it can require one-half a day or more just to mark the proper positions or locations for the seals on the shanks of four or more propeller blades for installation in a single propeller hub or barrel, or an hour or more for each blade. Additional time must be allowed for the adhesive to cure, which may extend to 24 hours or more. Yet, to this point there has not been a tool or gauge developed to assist in this task, even though a number of different tools, gauges, fixtures, and the like have been developed in the past for other propeller maintenance and repair operations.
Thus, a propeller blade seal positioning gauge solving the aforementioned problems is desired.